This invention relates to an improved, heavy duty, mechanical snubber, or shock absorbing strut. Such snubbers find important application in industry, and are widely employed in electric power generating plants to protect fluid carrying pipes from seismic shock, or from load transients introduced by flow variations resulting from turbine valve trip, water hammer, relief valve blow down or pump operation.
To accomodate the normal movement, such as expansion and contraction of high pressure, high temperature steam pipes, as used in nuclear power plants, where inherent temperature changes occur during operation, particularly during start-up or shut-down periods, it is customary to support such pipes from fixed structure, such as power plant walls or ceilings, by yieldable means which freely permit such movement. However, in the event of seismic or other transient shock, when the system or its support structure is subjected to vibratory motion or acceleration forces, such yieldable support means do not restrain rapid, large amplitude, relative movement between pipes and their support structure, which can result in rutpure of the pipes. To prevent such destructive movement, it is now customary to attach snubbers between the pipes and their support structure. It is the function of these snubbers to permit the relatively slow pipe movements that result from normal thermal expansion and contraction, but to offer substantial resistance (damping) to rapid changes in spacing between the pipes and the support structures.
Although the prior art discloses numerous snubbers and shock absorbers which function to damp or limit effects of sudden shock and vibration, all have features which make them unduly complex and expensive to produce, or which render them unsuited for use in power plants where they are installed in high temperature and, possibly, radiation environments. In such environments, hydraulic type snubbers have been found to be unsuitable, with the result that development has focused on snubbers that involve only mechanical mechanisms. Many of these prior mechanical snubbers employ rotatable inertial masses which are driven into rotation or rotational oscillation by seismic shock or vibration, the inertia of the inertial mass acting to restrain or damp the speed, acceleration and amplitude of movements resulting from forces applied to the snubber. However, in known prior devices of this mechanical type, the inertia effects of the inertial mass have been insufficient to provide the accurate damping or restraint desired, and it has been necessary to include auxiliary damping such as might be provided by an associated friction braking device. Often, such friction braking devices are actuated through other mechanisms, including one or more inertial masses, and involving still other moving parts such as springs and friction clutches. In addition to adding to snubber complexity and cost of manufacture, the effectiveness of friction brakes, springs and friction clutches, tends to vary with wear and environmental conditions, particularly temperature and radiation.
In contrast, the snubber of the present invention requires no friction braking devices, no springs and no friction clutches. It relies solely on the known physical constants of one or more pivoted masses, having a predetermined effective mass, which are driven into oscillatory rotation by external forces applied to the snubber.
The present invention has advantages over the snubber disclosed in the co-pending patent application of Richard A. Calabrese, Ser. No. 897,102, filed Apr. 17, 1978, and of common assignee herewith. That application is directed to a snubber in which relative axial movement between the support and load ends of a telescoping snubber is converted into rotary motion by means of a driving rack and driven worm arrangement. Rotation of the worm, caused by axial motion of the rack, effects, through the agency of a crank arrangement, oscillatory rotation of an inertial mass. Work done in accelerating, decelerating, and reversing the rotation of the inertial mass acts to resist, or damp, forces applied to the snubber.